Based on kernel version 4.16.1. Page generated on 2018-04-09 11:52 EST.
1 * Power State Coordination Interface (PSCI) 2 3 Firmware implementing the PSCI functions described in ARM document number 4 ARM DEN 0022A ("Power State Coordination Interface System Software on ARM 5 processors") can be used by Linux to initiate various CPU-centric power 6 operations. 7 8 Issue A of the specification describes functions for CPU suspend, hotplug 9 and migration of secure software. 10 11 Functions are invoked by trapping to the privilege level of the PSCI 12 firmware (specified as part of the binding below) and passing arguments 13 in a manner similar to that specified by AAPCS: 14 15 r0 => 32-bit Function ID / return value 16 {r1 - r3} => Parameters 17 18 Note that the immediate field of the trapping instruction must be set 19 to #0. 20 21 22 Main node required properties: 23 24 - compatible : should contain at least one of: 25 26 * "arm,psci" : For implementations complying to PSCI versions prior 27 to 0.2. 28 For these cases function IDs must be provided. 29 30 * "arm,psci-0.2" : For implementations complying to PSCI 0.2. 31 Function IDs are not required and should be ignored by 32 an OS with PSCI 0.2 support, but are permitted to be 33 present for compatibility with existing software when 34 "arm,psci" is later in the compatible list. 35 36 * "arm,psci-1.0" : For implementations complying to PSCI 1.0. 37 PSCI 1.0 is backward compatible with PSCI 0.2 with 38 minor specification updates, as defined in the PSCI 39 specification[2]. 40 41 - method : The method of calling the PSCI firmware. Permitted 42 values are: 43 44 "smc" : SMC #0, with the register assignments specified 45 in this binding. 46 47 "hvc" : HVC #0, with the register assignments specified 48 in this binding. 49 50 Main node optional properties: 51 52 - cpu_suspend : Function ID for CPU_SUSPEND operation 53 54 - cpu_off : Function ID for CPU_OFF operation 55 56 - cpu_on : Function ID for CPU_ON operation 57 58 - migrate : Function ID for MIGRATE operation 59 60 Device tree nodes that require usage of PSCI CPU_SUSPEND function (ie idle 61 state nodes, as per bindings in [1]) must specify the following properties: 62 63 - arm,psci-suspend-param 64 Usage: Required for state nodes[1] if the corresponding 65 idle-states node entry-method property is set 66 to "psci". 67 Value type: <u32> 68 Definition: power_state parameter to pass to the PSCI 69 suspend call. 70 71 Example: 72 73 Case 1: PSCI v0.1 only. 74 75 psci { 76 compatible = "arm,psci"; 77 method = "smc"; 78 cpu_suspend = <0x95c10000>; 79 cpu_off = <0x95c10001>; 80 cpu_on = <0x95c10002>; 81 migrate = <0x95c10003>; 82 }; 83 84 Case 2: PSCI v0.2 only 85 86 psci { 87 compatible = "arm,psci-0.2"; 88 method = "smc"; 89 }; 90 91 Case 3: PSCI v0.2 and PSCI v0.1. 92 93 A DTB may provide IDs for use by kernels without PSCI 0.2 support, 94 enabling firmware and hypervisors to support existing and new kernels. 95 These IDs will be ignored by kernels with PSCI 0.2 support, which will 96 use the standard PSCI 0.2 IDs exclusively. 97 98 psci { 99 compatible = "arm,psci-0.2", "arm,psci"; 100 method = "hvc"; 101 102 cpu_on = < arbitrary value >; 103 cpu_off = < arbitrary value >; 104 105 ... 106 }; 107 108 [1] Kernel documentation - ARM idle states bindings 109 Documentation/devicetree/bindings/arm/idle-states.txt 110 [2] Power State Coordination Interface (PSCI) specification 111 http://infocenter.arm.com/help/topic/com.arm.doc.den0022c/DEN0022C_Power_State_Coordination_Interface.pdf